Mercury bioaccumulation and effects on birds in San Francisco Bay

Highlights

• San Francisco Bay is an important wintering and breeding ground for more than 1 million waterbirds annually
• Mercury concentrations are highest in birds that eat fish and that reside in the Lower South Bay
• When Forster’s terns arrive in the Bay in spring to breed, mercury concentrations in their blood increase by four-fold in a six week period
• Based on mercury concentrations in blood, nearly 60% of all breeding Forster’s terns sampled in the Bay are at high risk of toxic effects
• One important piece of evidence of impairment of reproduction in Forster’s terns is that average mercury concentrations in failed to-hatch eggs were statistically significantly higher than in randomly selected eggs
• Avian eggs represent an ideal matrix for assessing bioaccumulation because they are indicative of short-term, localized exposure and are central to predicting risk in multiple lifestages